Micromachined piezoelectric membranes with high nominal quality factors in newtonian liquid media: A Lamb's model validation at the microscale

Although extensively presented as one of the most promising silicon-based micromachined sensor adapted to real-time measurements in liquid media, the cantilevered structure still suffers from its quality factor (Q) dramatic dependence on the liquid viscosity thus lowering the measurement resolution. In this paper, micromachined piezoelectric membranes are introduced as a potential alternative to the cantilevers for biological applications. High Q-factors (up to 150) of micromachined piezoelectric membranes resonating in various liquid mixtures (water/glycerol and water/ethanol) are thus reported and a theoretical model proposed by Lamb [H. Lamb, On the vibrations of an elastic plate in contact with water, Proc. Roy. Soc. Lond. A 98 (1920) 205-216] is validated for microscale structures proving that the variation of the liquid viscosity (if lower than 10 cP) has no effect on the dynamic behavior of the membranes. To conclude, two types of experiments were performed in water/glycerol mixtures: in-flow (with liquid continuously flowing on the devices) and in-spot (with individual membranes oscillating in a 5 mu L volume of liquid). The results interestingly showed that for the in-spot configuration the-Q-factor values are more than two-fold the ones corresponding to in-flow measurements thus providing alternative insights into the way to conceive ideal configurations for real-time biological measurements in liquid media. (C) 2006 Elsevier B.V. All rights reserved.